Environmentally-Friendly Multi-Layer Flexible Film Having Barrier Properties

ABSTRACT

A multi-layer film with barrier properties having one or more layers made from a bio-based film is disclosed. In one aspect, the print web comprises a bio-based film. The bio-based film can comprises polylactide or polyhydroxy-alkanoate. Unlike prior art petroleum-based films, the bio-based film of the present invention is made from a renewable resource and is biodegradable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a biodegradable, bio-based flexiblepackaging material that can be used in packaging food products and to amethod of making the bio-based packaging material. More specifically itrelates to using a biodegradable plastic made from a renewable source asat least one of the layers in the multi-layer flexible film.

2. Description of Related Art

Multi-layered film structures made from petroleum-based productsoriginating from fossil fuels are often used in flexible packages wherethere is a need for its advantageous barrier, sealant, andgraphics-capability properties. Barrier properties in one or more layersare important in order to protect the product inside the package fromlight, oxygen or moisture. Such a need exists, for example, for theprotection of foodstuffs, which may run the risk of flavor loss,staling, or spoilage if insufficient barrier properties are present toprevent transmission of such things as light, oxygen, or moisture intothe package. In addition, barrier properties also prevent undesirableleaching of the product to the outside of the bag. For example, oilyfoods such as potato chips have the potential for some oil to leach outinto the film of the bag. The sealant properties are important in orderto enable the flexible package to form an airtight or hermetic seal.Without a hermetic seal, any barrier properties provided by the film areineffective against oxygen, moisture, or aroma transmission between theproduct in the package and the outside. A graphics capability is neededbecause it enables a consumer to quickly identify the product that he orshe is seeking to purchase, allows food product manufacturers a way tolabel the nutritional content of the packaged food, and enables pricinginformation, such as bar codes to be placed on the product.

One prior art multi-layer or composite film used for packaging potatochips and like products is illustrated in FIG. I which is a schematic ofa cross section of the multi-layer film 100 illustrating each individualsubstantive layer. Each of these layers functions in some way to providethe need barrier, sealant, and graphics capability properties. Forexample, the graphics layer 114 is typically used for the presentationof graphics that can be reverse-printed and viewed through a transparentouter base layer 112. Like numerals are used throughout this descriptionto describe similar or identical parts, unless otherwise indicated. Theouter base layer 112 is typically oriented polypropylene (“OPP”) orpolyethylene terephthalate (“PET”). A metal layer disposed upon an innerbase layer 118 provides the required barrier properties. It has beenfound and is well-known in the prior art that by metallizing apetroleum-based polyolefin such as OPP or PET reduces the moisture andoxygen transmission through the film by approximately three orders ofmagnitude. Petroleum-based OPP is typically utilized for the base layers112 118 because of its lower cost. A sealant layer 119 disposed upon theOPP layer 118 enables a hermetic seal to be formed at a temperaturelower than the melt temperature of the OPP. A lower melting pointsealant layer 119 is desirable because melting the metallized OPP toform a seal could have an adverse effect on the barrier properties.Typical prior art sealant layers 119 include an ethylene-propyleneco-polymer and an ethylene-propylene-butene-1 ter-polymer. A glue orlaminate layer 115, typically a polyethylene extrusion, is required toadhere the outer base layer 112 with the inner, product-side base layer118. Thus, at least two base layers of petroleum-based polypropylene aretypically required in a composite or multi-layered film.

Other materials used in packaging are typically petroleum-basedmaterials such as polyester, polyolefin extrusions, adhesive laminates,and other such materials, or a layered combination of the above.

FIG. 2 demonstrates schematically the formation of material, in whichthe OPP layers 112, 118 of the packaging material are separatelymanufactured, then formed into the final material 100 on an extrusionlaminator 200. The OPP layer 112 having graphics 114 previously appliedby a known graphics application method such as flexographic orrotogravure is fed from roll 212 while OPP layer 118 is fed from roll218. At the same time, resin for PE laminate layer 115 is fed intohopper 215 a and through extruder 215 b, where it will be heated toapproximately 600° F. and extruded at die 215 c as molten polyethylene115. This molten polyethylene 115 is extruded at a rate that iscongruent with the rate at which the petroleum-based OPP materials 112,118 are fed, becoming sandwiched between these two materials. Thelayered material 100 then runs between chill drum 220 and nip roller230, ensuring that it forms an even layer as it is cooled, The pressurebetween the laminator rollers is generally set in the range of 0.5 to 5pounds per linear inch across the width of the material. The large chilldrum 220 is made of stainless steel and is cooled to about 50-60° F., sothat while the material is cooled quickly, no condensation is allowed toform. The smaller nip roller 230 is generally formed of rubber oranother resilient material. Note that the layered material 100 remainsin contact with the chill drum 220 for a period of time after it haspassed through the rollers, to allow time for the resin to coolsufficiently. The material can then be wound into rolls (notspecifically shown) for transport to the location where it will be usedin packaging. Generally, it is economical to form the material as widesheets that are then slit using thin slitter knives into the desiredwidth as the material is rolled for shipping.

Once the material is formed and cut into desired widths, it can beloaded into a vertical form, fill, and seal machine to be used inpackaging the many products that are packaged using this method. FIG. 3shows an exemplary vertical form, fill, and seal machine that can beused to package snack foods, such as chips. This drawing is simplified,and does not show the cabinet and support structures that typicallysurround such a machine, but it demonstrates the working of the machinewell. Packaging film 310 is taken from a roll 312 of film and passedthrough tensioners 314 that keep it taut. The film then passes over aformer 316, which directs the film as it forms a vertical tube around aproduct delivery cylinder 318. This product delivery cylinder 318normally has either a round or a somewhat oval cross-section. As thetube of packaging material is pulled downward by drive belts 320, theedges of the film are sealed along its length by a vertical sealer 322,forming a back seal 324. The machine then applies a pair of heat-sealingjaws 326 against the tube to form a transverse seal 328. This transverseseal 328 acts as the top seal on the bag 330 below the sealing jaws 326and the bottom seal on the bag 332 being filled and formed above thejaws 326. After the transverse seal 328 has been formed, a cut is madeacross the sealed area to separate the finished bag 330 below the seal328 from the partially completed bag 332 above the seal. The film tubeis then pushed downward to draw out another package length. Before thesealing jaws form each transverse seal, the product to be packaged isdropped through the product delivery cylinder 318 and is held within thetube above the transverse seal 328.

Petroleum-based prior art flexible films comprise a relatively smallpart of the waste produced when compared to other types of packaging.Thus, it is uneconomical to recycle because of the energy required tocollect, separate, and clean the used flexible film packages. Further,because the petroleum films are environmentally stable, petroleum basedfilms have a relatively low rate of degradation. Consequently, discardedpackages that become inadvertently dislocated from intended wastestreams can appear as unsightly litter for a relatively long period oftime. Further, such films can survive for long periods of time in alandfill. Another disadvantage of petroleum-based films is that they aremade from oil, which many consider to be a limited, non-renewableresource. Further, the price of petroleum-based films is volatile sinceit is tied to the price of oil. Consequently, a need exists for abiodegradable flexible film made from a renewable resource. In oneembodiment, such film should be food safe and have the requisite barrierproperties to store a low moisture shelf-stable food for an extendedperiod of time without the product staling. The film should have therequisite sealable and coefficient of friction properties that enable itto be used on existing vertical form, fill, and seal machines.

SUMMARY OF THE INVENTION

The present invention is directed towards a multi-layer film havingbarrier properties wherein one or more layers comprises a bio-basedfilm. In one aspect, the multi-layer packaging film of the presentinvention has an outer layer comprising a bio-based film, an adhesivelayer adhered to the outer layer and a product side layer having barrierproperties. In one aspect, the bio-based film is selected frompolylactide (PLA) and polyhydroxy-alkanoate (PHA). The present inventionthereby provides a multi-layer film with barrier properties that ismade, at least in part, from renewable resources. Further, in oneembodiment, at least a portion of the film is biodegradable. The aboveas well as additional features and advantages of the present inventionwill become apparent in the following written detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willhe best understood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 depicts a cross-section of an exemplary prior art packaging film;

FIG. 2 depicts the exemplary formation of a prior art packaging film;

FIG. 3 depicts a vertical form, fill, and seal machine that is known inthe prior art;

FIG. 4 depicts a magnified schematic cross-section of a hybridmulti-layer packaging film made according to one embodiment of theinvention; and

FIG. 5 depicts a magnified schematic cross-section of a multi-layerpackaging film made according to one embodiment of the invention.

DETAILED DESCRIPTION

The present invention is directed towards use of a bio-based film as atleast one of the film layers in a multi-layer flexible film packaging.As used herein, the term “bio-based film” means a polymer film made froma non-petroleum or biorenewable feedstock.

One problem with bio-based plastic films is that such films have poormoisture barrier and oxygen barrier properties. As a result, such filmscannot currently be used exclusively in packaging. Further, manybiodegradable films are brittle and stiffer than OPP typically used forflexible film packages. The handling of containers made exclusively frombiodegradable films is therefore relatively noisy as compared to priorart petroleum-based films. However, the inventors have discovered thatmany of these problems can minimized or eliminated by using a “hybrid”film.

FIG. 4 depicts a magnified schematic cross-section of a hybridmulti-layer packaging film made according to one embodiment of theinvention. Here, the outer transparent base layer comprises abiodegradable, bio-based film 402 in place of an orientedpetroleum-based polypropylene 112 depicted in FIG. 1.

In one embodiment, the biodegradable, bio-based film 402 comprisespolylactic acid, also known as polylactide (“PLA”), which is abiodegradable, thermoplastic, aliphatic polyester derived from lacticacid. PLA can be easily produced in a high molecular weight form throughring-opening polymerization of lactide/lactic acid to PLA by use of acatalyst and heat.

PLA can be made from plant-based feedstocks including soybeans, asillustrated by U.S. Patent Application Publication Number 20040229327 orfrom the fermentation of agricultural by-products such as corn starch orother plant-based feedstocks such as corn, wheat, or sugar beets. PLAcan be processed like most thermoplastic polymers into a film. PLA hasphysical properties similar to PET and has excellent clarity. PLA filmsare described in U.S. Pat. No. 6,207,792 and PLA resins are availablefrom Natureworks LLC (http://www.natureworkslle.com) of Minnetonka,Minn. PLA degrades into carbon dioxide and water.

In one embodiment, the biodegradable, bio-based film 402 comprisespolyhydroxy-alkanoate (“PHA”), available from Archer Daniels Midland ofDecatur, Ill. PHA is a polymer belonging to the polyesters class and canbe produced by microorganisms (e.g. Alcaligenes eutrophus) as a form ofenergy storage. In one embodiment, microbial biosynthesis of PHA startswith the condensation of two molecules of acetyl-CoA to giveacetoacetyl-CoA which is subsequently reduced to hydroxybutyryl-CoA.Hydroxybutyryl-CoA is then used as a monomer to polymerize PHB, the mostcommon type of PHA.

The laminate film depicted in FIG. 4 can be made by extruding abiodegradable bio-based film 402 into a film sheet. In one embodiment,the bio-based film 402 has been oriented in the machine direction or thetransverse direction. In one embodiment, the bio-based film 402comprises a biaxially oriented film. In one embodiment, a 120 gauge PLAfilm 402 is made. A graphic image 114 is reverse printed onto thebiodegradable, bio-based film 402 by a known graphics application methodsuch as flexographic or rotogravure to form a graphics layer 114. Thisgraphics layer 114 can then be “glued” to the product-side metalized OPPfilm 118, by a laminate layer 115, typically a polyethylene extrusion.Thus, the prior art OPP print web is replaced with a biodegradable printweb. In one embodiment, the bio-based film 402 comprises multiple layersto enhance printing and coefficient of friction properties. In oneembodiment, the bio-based film 402 comprises one or more layers of PLA.

In the embodiment shown in FIG. 4, the inside sealant layer 119 can befolded over and then sealed on itself to form a tube having a fin sealfor a backseal. The fin seal is accomplished by the application of heatand pressure to the film. Alternatively, a thermal stripe can beprovided on the requisite portion of the bio-based film 402 to permit alap seal to be used.

Examples of metalized OPP films 118 having a sealant layer 119 that canbe used in accordance with the present invention include PWX-2, PWX-4,PWS-2 films available from Toray Plastics of North Kingstown, R.I. orMU-842, Met RB, or METALLYTE films available from Exxon-Mobil Chemical.

The laminate of film depicted in FIG. 4 is a hybrid film because itcomprises both a biodegradable, bio-based film 402 and a stable,metalized OPP film 118. However, one benefit of the present invention isthat the outer PLA film 402 can be made thicker than prior art outerfilms to maximize the use of bio-based films 402 and thebiodegradability of the overall package while preserving “bag feel”properties that consumers have become so well known to consumers. Forexample, whereas the prior art outside film 112, laminate layer 115 andinner base layer 118 roughly were each one-third of the package film byweight, in one embodiment, the laminate of the present inventioncomprises an outside bio-based film 402 of 50% by weight, a laminatelayer 115 being 20% by weight and an inner base OPP layer 118 of about30% by weight of the total packaging film. Consequently, less OPP film118 can be used than is required in the prior art reducing consumptionof fossil fuel resources. In one embodiment, the present inventionprovides a hybrid film having at least about one-quarter less andpreferably between about one-third and one-half less fossil fuel-basedcarbon than a prior art film, yet comprises acceptable barrierproperties. As used herein, a film having acceptable oxygen barrierproperties has an oxygen transmission rate of less than about 150cc/m²/day. As used herein, a film having acceptable moisture barrierproperties comprises a water vapor transmission rate of less than about5 grams/m²/day.

There are several advantages provided by the hybrid film depicted inFIG. 4. First, the inventors have discovered that biodegradable films402 such as PLA make excellent print webs. Unlike polypropylene, PLA hasoxygen in the backbone of the molecule. The oxygen inherently provideshigh surface energy that facilitates ink adhesion, thereby reducing theamount of pre-treatment required to prepare the film for print ascompared to prior art petroleum-based OPP films. Second, the film can beproduced using the same existing capital assets that are used to makeprior art films. Third, the hybrid film uses 25% to 50% less petroleumthan prior art films. Fourth, the film is partially degradable which canhelp to reduce unsightly litter.

FIG. 5 depicts a magnified schematic cross-section of a multi-layerpackaging film made according to one embodiment of the invention. Here,the inner base layer comprises a thin metalized barrier/adhesionimproving film layer 416 adjacent to a biodegradable, bio-based film 418such as PLA instead of an oriented polypropylene 118 depicted in FIG. 1and FIG. 4.

A tie layer (not shown) can be disposed between the metalizedbarrier/adhesion improving film layer 416 and the bio-based film layer418. A tie layer can permit potentially incompatible layers to be bondedtogether. The tie layer can be selected from maleic anhydride,ethylenemethacrylate (“EMA”), and ethylenevinylacetate (“EVA”).

The metalized barrier/adhesion improving film layer 416 adjacent to thebio-based film 418 can be one or more polymers selected frompolypropylene, an ethylene vinyl alcohol (“EVOH”) formula, polyvinylalcohol (“PVOH”), polyethylene, polyethylene terephthalate, nylon, and anano-composite coating.

Below depicts EVOH formulas in accordance with various embodiments ofthe present invention.

The EVOH formula used in accordance with the present invention can rangefrom a low hydrolysis EVOH to a high hydrolysis EVOH. As used herein alow hydrolysis EVOH corresponds to the above formula wherein n=25. Asused herein, a high hydrolysis EVOH corresponds to the above formulawherein n=80. High hydrolysis EVOH provides oxygen barrier propertiesbut is more difficult to process. When metalized, EVOH providesacceptable moisture barrier properties. The EVOH formula can becoextruded with the PLA 418 and the EVOH formula can then be metalizedby methods known in the art including vacuum deposition.

In one embodiment, the metalized film 416 comprises a metalized PET 416that is less than about 10 gauge and preferably between about 2 andabout 4 gauge in thickness. The PET can be coextruded with the PLA 418and the PET can then be metalized by methods known in the art. In oneembodiment, the metalized film 416 comprises a PVOH coating that isapplied to the PLA as a liquid and then dried.

In one embodiment, one or both bio-based films 402 418 consists of onlyPLA. Alternatively, additives can be added to the print web bio-basedfilm 402 or the barrier web bio-based film 418 during the film makingprocess to improve film properties such as the rate of biodegradation.For example, the rate of degradation of biodegradable PLA is relativelyslow. Consequently, pieces of litter are still visible for a period oftime. To accelerate breakdown of PLA, starch can be added to the basepolymer to improve the biodegradability of the final film. In oneembodiment, one or both bio-based films 402 418 comprises about 1% toabout 20% starch by weight of the film. The starch will cause theoriented PLA film to breakdown into smaller pieces (roughly akin to onechewing food). These smaller pieces will then be far less visible in theenvironment as litter and will as degrade faster due to the largersurface area because the larger edge area allows moisture to seep inbetween the multi-layer film layers and breaks down the layers faster. APLA based film ultimately breaks down into CO₂ and H₂O.

Similar results can be achieved by adding various Transition metalstereates (Cobalt, Nickel, etc) but use of a starch would be preferredas it would also break down and leave no residual. In one embodiment,one or both bio-based films 402 418 comprises up to about 5% of astearate additive by weight of the film. One or more stearate additivescan be selected from aluminum, antimony, barium, bismuth, cadmium,cerium, chromium, cobalt, copper, gallium, iron, lanthanum, lead,lithium, magnesium, mercury, molybdenum, nickel, potassium, rare earths,silver, sodium, strontium, tin, tungsten, vanadium, yttrium, zinc orzirconium. Such additives are marketed under the TDPA tradename and areavailable from EPI of Conroe, Tex., USA. In one embodiment, one or bothbio-based films 402 418 comprises a photocatalyst. Photocatalysts areknown in the art and are typically used in 6-pack beverage can containerrings to facilitate breakdown upon exposure to sunlight.

Further, one or more suitable co-polymer additives can be used selectedfrom ethylene methylacrylate and styrene-butydiene block co-polymer(e.g., tradename KRATON) as a compatilizer to improve the degree ofcompatibility between the bio-based film 402 418 and other film layers.For example, such co-polymer additives can be used to improve the heatseal characteristics of the laminate film. The co-polymer additives canalso improve the lamination bond strength to help the biodegradable filmprint web to better adhere to an OPP barrier web, or to help thebio-based film print web to better adhere to a bio-based barrier web.Additives can also be used such that a biodegradable adhesive, e.g., thelaminate layer, can be used. In one embodiment, the multi-layer filmcomprises a bio-based adhesive. Such additives can also help to metalizea biodegradable film via conventional aluminum vapor depositionprocesses to make a biodegradable barrier web that provides barrierperformance for the biodegradable film. Biodegradable films arenotorious for having poor barrier properties. As used herein, the term“additives” is not limited to chemical additives and can include surfacetreatment including, but not limited to, corona treatment.

In one embodiment, the bio-based film comprises a nanocomposite ornanocomposite coating to provide barrier protection. Nanocomposites areknown in the art as exemplified by U.S. Patent application PublicationNo. 2005/0096422, which is hereby incorporated by reference. In oneembodiment, the bio-based film comprises a nanoclay to provide barrierproperties. Nanoclays in accordance with the present invention compriselayered silicate platelets such as vermiculite, aluminosilicates,zeolites, bentonite, montmorillonite, kaolinite, nontronite, beidellite,volkonskoite, hectorite, sponite, laponite, sauconite, hydrous mica,chlorite, magadiite, kenyaite, ledikite and mixtures thereof.

In one embodiment, a nanoclay can be added in the same type of graphicsapplication method presently used to apply an ink layer to a web offilm. U.S. Pat. No. 6,232,389, for example, discloses a coatingcomposition which contains substantially dispersed exfoliated layeredsilicates in an elastomeric polymer that can be applied as a coating anddried. The free oxygen of PLA means that it has a natural affinity forapplication of such coatings. In one embodiment, the nanoclay is addedto the bio-based film as an additive during film production.

In one embodiment, the layered silicate platelets of the nanocompositecomprise an aluminum-silicate that forms a substantially cylindrical orspherical structure. Hundreds of these structures can be coupledtogether can form long, thin tubes that are very difficult for oxygen orwater molecules to penetrate. In one embodiment, the nanocompositecomprises a pore size sufficient such that the navigation of an oxygenand/or water molecule through the nanocomposite pore is sufficientlyretarded to preserve the shelf-life of a low moisture food ingredient,such as a potato chip for two or more months in a biodegradable laminatebag comprising a nanocomposite for barrier properties. In oneembodiment, the platelets are bound so tightly together that there arevirtually no tube openings for the oxygen or water molecules to enter,In one embodiment, the nanocomposite comprises a scavenger that reactswith oxygen or water. Consequently, in one embodiment, the nanocompositecomprises iron.

The present invention provides numerous advantages over traditional,petroleum-based prior art films. First, the present invention reducesconsumption of fossil fuels because a bio-based plastic is being usedfor one or more layers of the film that previously required apetroleum-based/fossil-fuel based polypropylene polymer. Consequentlythe film of the present invention is made with a renewable resource.

Second, the present invention lowers the amount of carbon dioxide in theatmosphere because the origin of the bio-based film is plant-based.Although the bio-based film can degrade into water and carbon dioxide ina relatively short period of time under composting conditions, if thefilm is placed into a landfill the carbon dioxide is effectivelysequestered away and stored because of the lack of light, oxygen, andmoisture available to degrade to the film. Thus, the carbon dioxide thatwas pulled from the atmosphere by the plant from which the bio-basedfilm was derived is effectively placed into storage.

Third, less litter is visible because a portion of the film making upthe resultant package is biodegradable. As used herein, the term“biodegradable” means that less than about 5% by weight and preferablyless than about 1% of the film remains after being left at 35° C. at 75%humidity in the open air for 60 days. Those skilled in the art willunderstand that at different ambient conditions, it may take longer forthe film to degrade. In one embodiment, less than 5% of the bio-basedfilm remains after being left at 25° C. and 50% relative humidity forfive years. By comparison, an OPP film can last more than 100 yearsunder these same conditions.

Fourth, energy is conserved because it takes less energy to create afilm in accordance with the present invention than prior art petroleumbased flexible films. For example 1 kg of PLA requires only 56megajoules of energy, which is 20% to 50% fewer fossil resources thanrequired to make petroleum-based plastics such as polypropylene.

Fifth, the invention provides more stable and less volatile pricing.Unlike petroleum-based commodities which fluctuate widely based upon theprice of oil, bio-based commodities are more stable and less volatile.Further, bio-based films have the potential to benefit from continualimprovements in genetically-engineered plants that can increase thedesired feedstock composition and yield.

While this invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

1. A multi-layer packaging film comprising: a) an outer layer comprisinga bio-based film; b) an adhesive layer adjacent to said outer layer; andc) a product side layer comprising barrier properties.
 2. The film ofclaim 1 wherein said bio-based film comprises polylactide.
 3. The filmof claim 1 wherein said bio-based film comprises polyhydroxy-alkanoate.4. The film of claim 1 wherein said bio-based film comprises at least25% of said multi-layer packaging film by weight.
 5. The film of claim 1wherein said bio-based film further comprises a graphic image.
 6. Thefilm of claim 1 wherein said bio-based film comprises between about 1%and about 20% starch by weight of the film.
 7. The film of claim 1wherein said bio-based film further comprises a stearate additive.
 8. Asnack food package made from a multi-layer flexible film having barrierproperties, said flexible film comprising a bio-based film.